Doerr is the best-known investor at Kleiner Perkins—and indeed, likely still the most famous venture capitalist in the world, having backed Amazon, Netscape, and Google in the 1990s, in a prescient bid that this Internet thing might amount to something.

For Doerr, this is a bold step that deeply increases his involvement in and commitment to the company, which had a slow start but is now seeing a dramatic increase in usage following the introduction of smartphone versions of its app, which was initially iPad-only. Doerr recently noted that the company is adding one user a second.

By taking the board seat, as opposed to assigning it to a less experienced partner, he is putting the full weight of his reputation behind Flipboard.

Flipboard confirmed that Doerr had joined its board, which also included Flipboard founder and CEO Mike McCue and Index Ventures partner Danny Rimer.

Doerr is no stranger to the company, of course, which has been one of Kleiner's more prominent bets on social and mobile media.

"John has always been interested and around and helpful," says Marci McCue, Flipboard's vice president of marketing. For example, Doerr attended Flipboard's launch in July 2010. (Marci and Mike McCue are married.)

Doerr and Mike McCue have a long professional acquaintance going back two decades. McCue sold a company to Netscape, where Doerr was an investor and board member, and subsequently started an Internet-telephony company, Tellme, also with Doerr and Kleiner's backing.